Kineta (KANT) 10-Q 10 Nov 16 2016 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Nov. 08, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Trading Symbol	PTI
Entity Registrant Name	PROTEOSTASIS THERAPEUTICS, INC.
Entity Central Index Key	1,445,283
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		24,960,243

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 43,828	$ 13,844
Short-term investments	56,412
Accounts receivable	445	918
Other current assets	2,388	180
Total current assets	103,073	14,942
Property and equipment, net	342	566
Deferred offering costs		2,744
Other assets	81	144
Restricted cash	294	294
Total assets	103,790	18,690
Current liabilities:
Accounts payable	2,809	3,330
Accrued expenses	4,182	2,248
Deferred revenue	4,683	4,076
Deferred rent	196	182
Total current liabilities	11,870	9,836
Deferred revenue, net of current portion	1,666	4,265
Deferred rent, net of current portion	139	287
Preferred stock warrant liability		110
Derivative liability	142	2
Total liabilities	13,817	14,500
Commitments and contingencies (Note 9)
Convertible preferred stock, (Series A and B), $0.001 par value; 0 and 110,057,398 shares authorized as of September 30, 2016 and December 31, 2015, respectively; 0 and 104,854,769 shares issued and outstanding as of September 30, 2016 and December 31, 2015, respectively; aggregate liquidation preference of $0 and $149,392, respectively, as of September 30, 2016 and December 31, 2015		112,292
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value; 5,000,000 and 0 shares authorized as of September 30, 2016 and December 31, 2015, respectively; no shares issued and outstanding as of September 30, 2016 and December 31, 2015
Common stock, $0.001 par value; 125,000,000 and 170,000,000 shares authorized as of September 30, 2016 and December 31, 2015, respectively; 24,945,125 and 571,137 shares issued and outstanding as of September 30, 2016 and December 31, 2015, respectively	26	1
Additional paid-in capital	237,989	12,115
Accumulated other comprehensive loss	(9)
Accumulated deficit	(148,033)	(120,218)
Total stockholders’ equity (deficit)	89,973	(108,102)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 103,790	$ 18,690

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Convertible preferred stock (Series A and B), par value	$ 0.001	$ 0.001
Convertible preferred stock (Series A and B), shares authorized	0	110,057,398
Convertible preferred stock (Series A and B), shares issued	0	104,854,769
Convertible preferred stock (Series A and B), shares outstanding	0	104,854,769
Convertible preferred stock (Series A and B), aggregate liquidation preference	$ 0	$ 149,392
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	170,000,000
Common stock, shares issued	24,945,125	571,137
Common stock, shares outstanding	24,945,125	571,137

Statements of Operations

Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 1,715	$ 1,201	$ 4,324	$ 3,078
Operating expenses:
Research and development	9,218	6,258	23,498	16,737
General and administrative	3,266	1,523	8,682	4,553
Total operating expenses	12,484	7,781	32,180	21,290
Loss from operations	(10,769)	(6,580)	(27,856)	(18,212)
Interest income	36		56
Interest expense		(189)		(599)
Other expense, net	(38)	(281)	(15)	(598)
Net loss	(10,771)	(7,050)	(27,815)	(19,409)
Modification of Series A preferred stock		174		10,739
Accruing dividends on preferred stock		(2,459)	(1,378)	(6,698)
Net loss attributable to common stockholders	$ (10,771)	$ (9,335)	$ (29,193)	$ (15,368)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.54)	$ (16.77)	$ (1.75)	$ (28.05)
Weighted average common shares outstanding—basic and diluted	20,073,685	556,567	16,672,368	547,816

Statements of Comprehensive Los

Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,771)	$ (7,050)	$ (27,815)	$ (19,409)
Other comprehensive loss:
Unrealized loss on investments	(9)		(9)
Comprehensive loss	$ (10,780)	$ (7,050)	$ (27,824)	$ (19,409)

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - 9 months ended Sep. 30, 2016 - USD ($) $ in Thousands	Total	Initial Public Offering [Member]	Follow-on Public Offering [Member]	Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]Initial Public Offering [Member]	Common Stock [Member]Follow-on Public Offering [Member]	Common Stock [Member]Series A Preferred Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Initial Public Offering [Member]	Additional Paid-in Capital [Member]Follow-on Public Offering [Member]	Additional Paid-in Capital [Member]Series A Preferred Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2015	$ (108,102)			$ 112,292	$ 1				$ 12,115					$ (120,218)
Beginning balance, shares at Dec. 31, 2015	571,137			104,854,769	571,137
Exercise of stock options	$ 144								144
Exercise of stock options, shares					61,325
Stock-based compensation expense	1,245								1,245
Issuance of common stock upon completion of public offering, net of offering costs		$ 42,529	$ 69,469			$ 6	$ 6			$ 42,523	$ 69,463
Issuance of common stock upon completion of public offering, net of offering costs, shares						6,250,000	5,750,000
Conversion of convertible preferred stock to common stock	112,292			$ (112,292)	$ 10				112,282
Conversion of convertible preferred stock to common stock, shares				(104,854,769)	9,699,600
Issuance of common stock to settle accruing dividends								$ 3				$ (3)
Issuance of common stock to settle accruing dividends, Shares								2,590,742
Issuance of common stock for partial payment of accrued bonus	62								62
Issuance of common stock for partial payment of accrued bonus, shares					10,218
Conversion of preferred stock warrant to common stock warrant	28								28
Issuance of common stock for payment of consulting services	130								130
Issuance of common stock for payment of consulting services, shares					12,103
Other comprehensive loss	(9)												$ (9)
Net loss	(27,815)													(27,815)
Ending balance at Sep. 30, 2016	$ 89,973				$ 26				$ 237,989				$ (9)	$ (148,033)
Ending balance, shares at Sep. 30, 2016	24,945,125				24,945,125

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net loss	$ (27,815)	$ (19,409)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	248	199
Premium on short-term investments	(124)
Amortization of premium on short-term investments	2
Non-cash rent expense	(134)	(20)
Non-cash interest expense		599
Stock-based compensation expense	1,375	161
Change in fair value of derivative liability	140	536
Change in fair value of preferred stock warrant liability	(82)	77
Gain on disposal of property and equipment	(13)
Changes in operating assets and liabilities:
Accounts receivable	473	203
Other current assets	(2,200)	80
Other assets	63	161
Accounts payable	390	1,172
Accrued expenses	1,849	349
Deferred revenue	(1,992)	3,002
Net cash used in operating activities	(27,820)	(12,890)
Cash flows from investing activities:
Purchases of short-term investments	(56,299)
Purchases of property and equipment	(32)	(233)
Proceeds received from sale of property and equipment	13
Net cash used in investing activities	(56,318)	(233)
Cash flows from financing activities:
Proceeds from issuance of common stock upon completion of initial public offering, net of commissions and underwriting discounts	46,500
Proceeds from issuance of common stock upon completion of follow-on public offering, net of commissions and underwriting discounts	70,265
Proceeds from issuance of Series B convertible preferred stock, net of issuance costs		21,090
Proceeds from issuance of convertible promissory notes		5,000
Proceeds from exercise of stock options	144	73
Net cash provided by financing activities	114,122	25,249
Net increase in cash and cash equivalents	29,984	12,126
Cash and cash equivalents at beginning of period	13,844	8,793
Cash and cash equivalents at end of period	43,828	20,919
Supplemental disclosure of non-cash investing and financing activities:
Conversion of convertible preferred stock into common stock	112,292
Issuance of common stock to settle accrued Series A preferred stock dividends	3
Issuance of common stock for partial payment of accrued bonus	62
Conversion of preferred stock warrants into common stock warrants	28
Modification of Series A preferred stock		(10,738)
Conversion of convertible notes into Series B preferred stock		15,798
Deferred offering costs included in accounts payable and accrued expenses	524	950
Initial Public Offering [Member]
Cash flows from financing activities:
Payments of public offering costs	(2,515)	$ (914)
Follow-on Public Offering [Member]
Cash flows from financing activities:
Payments of public offering costs	$ (272)

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2016
Organization Consolidation And Presentation Of Financial Statements Abstract
Nature of the Business	1. Nature of the Business Proteostasis Therapeutics, Inc. (the “Company”) was incorporated in Delaware on December 13, 2006. The Company is an innovative biopharmaceutical company committed to the discovery and development of novel therapeutics that treat diseases caused by an imbalance in the proteostasis network, a set of pathways that control protein biosynthesis, folding, trafficking and clearance. The Company’s initial therapeutic focus is on cystic fibrosis, which is caused by defects in the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein and insufficient CFTR protein function. The Company’s lead product candidate, PTI-428, is in early clinical development, and the Company’s other drug candidates are in the preclinical development and discovery phases. The Company has incurred losses from operations since its inception. As of September 30, 2016, the Company had an accumulated deficit of $148.0 million. The Company has primarily funded its operations with proceeds received from its initial public offerings and sale of convertible preferred stock. As of September 30, 2016, the Company expects that its cash, cash equivalents and short-term investments of $100.2 million will be sufficient to fund its operating expenses and capital requirements through the second quarter of 2018. Reverse Stock Split On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios. Public Offerings In February 2016, the Company issued and sold 6,250,000 shares of its common stock in its initial public offering (“IPO”) at a public offering price of $8.00 per share, for net proceeds of $42.5 million after deducting underwriting discounts and commissions of $3.5 million and other offering expenses of $4.0 million. Upon the closing of the IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 9,699,600 shares of common stock, and the Company issued 2,590,742 shares of common stock as payment of $36.0 million of accruing dividends due to holders of Series A preferred stock. In addition, the Company’s convertible preferred stock warrant outstanding at the close of the IPO converted to a warrant to purchase common stock. In connection with the completion of the IPO, the Company amended its certificate of incorporation to authorize the future issuance of up to 5,000,000 shares of undesignated preferred stock, par value $0.001 per share. As of September 30, 2016, there were no shares of preferred stock issued or outstanding. In September 2016, the Company issued and sold 5,750,000 shares of its common stock in a public offering at a public offering price of $13.00 per share, for net proceeds of $69.5 million after deducting underwriter discounts and commissions of $4.5 million and other offering expenses of $0.8 million. The foregoing includes the exercise by the underwriters of their options to purchase an additional 750,000 shares of our common stock within 30 days following the date of the final prospectus for the offering. Unaudited Interim Financial Information The accompanying unaudited interim financial statements as of September 30, 2016 and for the three months and nine months ended September 30, 2016 and 2015 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. The year-end balance sheet data was derived from the Company’s audited financial statements, but certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These interim financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2016.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, revenue recognition, the accrual for research and development expenses and the valuation of common stock, preferred stock warrant liability and derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. As of December 31, 2015, the Company had recorded $2.7 million of deferred offering costs in contemplation of the Company’s initial public offering. In conjunction with the completion of the IPO, the Company reclassified $4.0 million of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the IPO. In September 30, 2016, the Company reclassified $0.8 million of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the second public offering. Restricted Cash At September 30, 2016 and December 31, 2015, restricted cash consisted of a certificate of deposit collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities. Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of September 30, 2016, the Company’s cash equivalents consisted of money market funds and U.S. government-sponsored enterprise securities. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s derivative liability, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying value of cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. In connection with the automatic conversion of the Company’s convertible preferred stock, which occurred upon the listing of the Company’s common stock on the NASDAQ on February 10, 2016, the preferred stock warrant became a warrant to purchase common stock and the liability was remeasured at fair value and reclassified to additional paid-in capital. Net Income (Loss) per Share In February 2016, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 9,699,600 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net loss per share as the Company had issued shares that met the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred stock contractually entitled the holders of such shares to participate in dividends, but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not to have been issued if their effect is anti-dilutive. Recently Issued Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU No. 2016-02, Leases. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing (Topic 606) In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Short Term Investments

Short Term Investments	9 Months Ended
	Sep. 30, 2016
Cash Cash Equivalents And Short Term Investments [Abstract]
Short Term Investments	3. Short Term Investments Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, net of taxes, reported as a component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other expense, net. The following table summarizes the Company’s short term investments as of September 30, 2016 (in thousands): September 30, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 48,413 $ 2 $ (9 ) $ 48,406 U.S. treasury securities 8,008 — (2 ) 8,006 $ 56,421 $ 2 $ (11 ) $ 56,412 The Company did not have any realized gains or losses on its short-term investments for the three and nine months ended September 30, 2016. There were no other-than-temporary impairments recognized for the three and nine months ended September 30, 2016. The Company did not hold any short-term investments at or during the year ended December 31, 2015.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	4. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of September 30, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 24,366 $ — $ — $ 24,366 U.S. government-sponsored enterprise securities — 16,466 — 16,466 Short-term investments: U.S. government-sponsored enterprise securities — 48,406 — 48,406 U.S. treasury securities — 8,006 — 8,006 $ 24,366 $ 72,878 $ — $ 97,244 Liabilities: Derivative liability $ — $ — $ 142 $ 142 $ — $ — $ 142 $ 142 Fair Value Measurements as of December 31, 2015 Using: Level 1 Level 2 Level 3 Total Liabilities: Derivative liability $ — $ — $ 2 $ 2 Preferred stock warrant liability — — 110 110 $ — $ — $ 112 $ 112 The Company did not hold any cash equivalents or short-term investments as of December 31, 2015. During the periods ended September 30, 2016 and December 31, 2015, there were no transfers between Level 1, Level 2 and Level 3. Preferred Stock Warrant Liability The warrant liability in the table above is comprised of the fair value of a warrant for the purchase of Series A preferred stock and is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. On February 10, 2016, upon the closing of the IPO the Series A preferred stock converted into common stock, the preferred stock warrant became exercisable for common stock instead of preferred stock, and the preferred stock warrant liability, was remeasured at the fair value at that time, then reclassified to additional paid-in capital. The following assumptions and inputs were used in determining the fair value of the preferred stock warrant liability valued using the Black-Scholes option-pricing model: As As of December 31, 2016 2015 Expected term (in years) 2.25 2.5 Expected volatility 73.24% 59.12% Risk-free interest rate 0.74% 1.21% Expected dividend yield 8.0% 8.0% Derivative Liability The fair value of the derivative liability is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the derivative instrument was determined using the Monte-Carlo simulation analysis. In determining the fair value of the derivative liability, the inputs impacting fair value include the fair value of the Company’s common stock, expected term of the derivative instrument, expected volatility of the common stock price, risk-free interest rate, expected sales-based milestone payments, discount rate, probability of a change of control event, and the probability that the counterparty would elect to accept the alternative cash payment in lieu of its right to the future sales-based milestone payments. As of September 30, 2016, the Company determined the per share common stock price available based on publicly traded markets. As of December 31, 2015, the Company determined the per share fair value of the underlying stock price by taking into consideration recent business development and economic factors it deemed relevant. The Company determined the expected term of the instrument to be 2.50 years and 0.12 years as of September 30, 2016 and December 31, 2015, respectively. The Company estimated its expected stock volatility to be 81.5% and 74.1% as of September 30, 2016 and December 31, 2015, respectively, based on the historical volatility of publicly traded peer companies for terms matching the expected term of the instrument for each respective period. The risk-free interest rate was determined to be 0.82% and 0.14% as of September 30, 2016 and December 31, 2015, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. Changes in the values of the preferred stock warrant liability and the derivative liability are summarized below (in thousands): Preferred Stock Derivative Warrant Liability Liability Fair value at December 31, 2015 $ 110 $ 2 Change in fair value (82 ) 140 Conversion to common stock warrant (28 ) — Fair value at September 30, 2016 $ — $ 142

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2016
Text Block [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consisted of the following (in thousands): September 30, December 31, 2016 2015 Accrued payroll and related expenses $ 1,469 $ 1,607 Accrued research and development expenses 1,810 185 Accrued professional fees 711 436 Accrued other 192 20 $ 4,182 $ 2,248

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	6. Stock-Based Compensation 2016 Stock Option and Incentive Plan On February 3, 2016, the Company’s stockholders approved the 2016 Stock Option and Incentive Plan (the “2016 Plan”), which became effective on February 9, 2016. The 2016 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards and other stock-based awards. The number of shares initially reserved for issuance under the 2016 Plan is 1,581,839 shares. The number of shares of common stock that may be issued under the 2016 Plan will automatically increase on each January 1, beginning on January 1, 2017, by the lesser of 3% of the shares of the Company’s common stock outstanding on the immediately preceding December 31 or an amount determined by the Company’s board of directors or the compensation committee of the board of directors. The shares of common stock underlying any awards that are forfeited, canceled, repurchased or are otherwise terminated by the Company under the 2016 Plan and the 2008 Plan will be added back to the shares of common stock available for issuance under the 2016 Plan. 2016 Employee Stock Purchase Plan On February 3, 2016, the Company’s stockholders approved the 2016 Employee Stock Purchase Plan (the “2016 ESPP”), which became effective in connection with the completion of the Company’s initial public offering. A total of 138,757 shares of common stock were reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the 2016 ESPP will automatically increase on each January 1, beginning on January 1, 2017 and ending on January 1, 2026, by the least of (i) 138,757 shares of common stock, (ii) 1% of the Company’s shares of common stock outstanding on the immediately preceding December 31 and (iii) an amount determined by the Company’s board of directors or the compensation committee of the board of directors. Stock-Based Compensation The Company grants stock-based awards under the 2016 Plan and is authorized to issue common stock under the 2016 ESPP. The Company also has outstanding stock options under its 2008 Equity Incentive Plan, but is no longer granting awards under this plan. As of September 30, 2016, 1,260,609 shares of common stock were available for issuance under the 2016 Plan. As of September 30, 2016, 138,757 shares of common stock were available for issuance to participating employees under the 2016 ESPP. Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended September Nine Months Ended September 30, 2016 2015 2016 2015 Research and development $ 119 $ 63 $ 351 $ 2 General and administrative 451 60 1,024 159 $ 570 $ 123 $ 1,375 $ 161 Prior to 2013, the Company issued options to purchase 203,964 shares of common stock to non-employees, primarily members of the Company’s scientific advisory board, that vest upon the achievement of specified development and clinical milestones. As of September 30, 2016, options for the purchase of 83,250 shares held by non-employees remained unvested, pending achievement of the specified milestones, and had an aggregate fair value of $1.1 million. During the three and nine months ended September 30, 2015, the Company did not grant any options to non-employees. For the three and nine months ended September 30, 2016 the Company did not record any stock-based compensation expense for options granted to non-employees prior to 2013. For the three and nine months ended September 30, 2015 the Company recorded stock-based compensation expense for options granted to non-employees prior to 2013 of less than $(0.1) million and $(0.1) million, respectively. During the three and nine months ended September 30, 2016, the Company granted 12,103 shares of common stock to a non-employee as compensation under the Letter Agreement described in Note 10. For the three and nine months ended September 30, 2016, the Company recorded $0.1 million of stock-based compensation expense for shares granted to a non-employee. Stock-based compensation expense for the nine months ended September 30, 2015 was reduced by $0.5 million for the cumulative correction of immaterial errors associated with the recognition of stock-based compensation for certain stock options with performance-based vesting conditions. Of this amount, $0.2 million related to years prior to 2015 and $0.3 million related to the three months ended March 31, 2015. Based upon its evaluation of relevant factors, the Company concluded that the uncorrected errors in its previously issued financial statements for any of the periods affected are immaterial and that the impact of recording the cumulative correction during the nine months ended September 30, 2015 is not material to the Company’s results for the year ending December 31, 2015.

Collaboration Agreement

Collaboration Agreement	9 Months Ended
	Sep. 30, 2016
Organization Consolidation And Presentation Of Financial Statements Abstract
Collaboration Agreement	7. Collaboration Agreement Astellas In May 2016, the Company entered into a fourth amendment, effective as of January 31, 2016, to the Collaborative Research, Development, Commercialization and License Agreement (as further amended the “Astellas Agreement”) with Astellas Pharma Inc. (“Astellas”). In connection with the amendment, in June 2016 the Company received a payment of $1.0 million to conduct certain experiments in order to gain additional data on compounds being researched. The payment is being recognized by the Company as revenue over the three and a half year research term of the agreement, which commenced in January 2015, with a cumulative catch-up for the elapsed portion of the research term. In July 2016, the Company entered into a fifth amendment effective as of July 31, 2016, to the Astellas Agreement as a result of achieving a pre-clinical milestone and progressing to the optimization phase. These amendments provide for the Joint Research Committee to evaluate the progress at various intervals throughout the lead optimization phase. In connection with the amendment, the Company received a payment of a $0.8 million non-substantive milestone payment which is being recognized, over the three and half-year research term of the agreement, with a cumulative catch-up for the elapsed portion of the research term. Biogen In December 2015, the Company commenced the third year of the research term under the Collaborative Research, Development, Commercialization and License Agreement (the “Biogen Agreement”) with Biogen New Ventures (“Biogen”). Under the original terms of the agreement, beginning in the third year and continuing through the fourth year of the research term, the Company is entitled to receive reimbursement of costs incurred for actual full-time equivalent employees conducting research under the Biogen agreement. During the first two years of the research term the Company received research funding payments on a guaranteed basis in the amount of $4.0 million. The Company is not guaranteed to receive additional research funding payments throughout the remainder of the research term. Payments received as reimbursement for actual costs incurred will be accounted for in the same manner as the guaranteed research funding payments, such that the payments will be recognized over the four-year research term of the agreement, which commenced in December 2013, with a cumulative catch-up for the elapsed research term being recognized at the time any such payments are earned.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The Company did not record a federal or state income tax benefit for its losses for the nine months ended September 30, 2016 and 2015 due to the conclusion that a full valuation allowance is required against the Company’s deferred tax assets.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2016
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September Nine Months Ended September 30, 2016 2015 2016 2015 Numerator: Net loss $ (10,771 ) $ (7,050 ) $ (27,815 ) $ (19,409 ) Modification of Series A preferred stock — 174 — 10,739 Accruing dividends on preferred stock — (2,459 ) (1,378 ) (6,698 ) Net loss attributable to common stockholders-basic and diluted $ (10,771 ) $ (9,335 ) $ (29,193 ) $ (15,368 ) Denominator: Weighted average number of common shares outstanding—basic 20,073,685 556,567 16,672,368 547,816 Net loss per share attributable to common stockholders—basic and diluted $ (0.54 ) $ (16.77 ) $ (1.75 ) $ (28.05 ) The Company’s potential dilutive securities, which include stock options, convertible preferred stock as converted to common stock and a warrant to purchase preferred stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company has reported a net loss for all periods presented. Therefore, diluted net loss per common share is the same as basic net loss per common share. The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported As of September 30, 2016 2015 Convertible preferred stock (as converted to common stock) — 9,699,600 Options to purchase common stock 1,731,823 866,082 Warrant for the purchase of convertible preferred stock (as converted to common stock) 14,800 14,800 1,746,623 10,580,482

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Dr. Stelios Papadopoulos In May 2016 the Company entered into a Letter Agreement with Dr. Stelios Papadopoulos with an effective date of July 1, 2016 and a term of 36 months. Under the terms of the Letter Agreement, Dr. Papadopoulos will provide certain consulting and advisory services to the Company as and when requested. The Company will pay a quarterly retainer of $0.2 million to Dr. Papadopoulos for the duration of the Letter Agreement with aggregate fees totaling $2.5 million over the term of the Letter Agreement. The retainer may be paid in cash, common stock of the Company or a combination of the two at the discretion of the Company. Any common stock issued in settlement of payments due under this agreement will be valued at the average closing price of the stock for 20 trading days, as listed on the NASDAQ, ending three trading days prior to the issuance of the shares. Additionally, under the terms of the Letter Agreement, if the Company consummates a merger and acquisition (“M&A) transaction, as defined in the Letter Agreement, with another party during the term of the Agreement or the 12-month period following the expiration of the Letter Agreement, Dr. Papadopoulos will be entitled to a M&A transaction fee equal to 1% of the value of the transaction, as defined in the Letter Agreement.

Nature of the Business (Policie

Nature of the Business (Policies)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Reverse Stock Split	Reverse Stock Split On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios.
Public Offerings	Public Offerings In February 2016, the Company issued and sold 6,250,000 shares of its common stock in its initial public offering (“IPO”) at a public offering price of $8.00 per share, for net proceeds of $42.5 million after deducting underwriting discounts and commissions of $3.5 million and other offering expenses of $4.0 million. Upon the closing of the IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 9,699,600 shares of common stock, and the Company issued 2,590,742 shares of common stock as payment of $36.0 million of accruing dividends due to holders of Series A preferred stock. In addition, the Company’s convertible preferred stock warrant outstanding at the close of the IPO converted to a warrant to purchase common stock. In connection with the completion of the IPO, the Company amended its certificate of incorporation to authorize the future issuance of up to 5,000,000 shares of undesignated preferred stock, par value $0.001 per share. As of September 30, 2016, there were no shares of preferred stock issued or outstanding. In September 2016, the Company issued and sold 5,750,000 shares of its common stock in a public offering at a public offering price of $13.00 per share, for net proceeds of $69.5 million after deducting underwriter discounts and commissions of $4.5 million and other offering expenses of $0.8 million. The foregoing includes the exercise by the underwriters of their options to purchase an additional 750,000 shares of our common stock within 30 days following the date of the final prospectus for the offering.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited interim financial statements as of September 30, 2016 and for the three months and nine months ended September 30, 2016 and 2015 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. The year-end balance sheet data was derived from the Company’s audited financial statements, but certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These interim financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2016.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, revenue recognition, the accrual for research and development expenses and the valuation of common stock, preferred stock warrant liability and derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. As of December 31, 2015, the Company had recorded $2.7 million of deferred offering costs in contemplation of the Company’s initial public offering. In conjunction with the completion of the IPO, the Company reclassified $4.0 million of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the IPO. In September 30, 2016, the Company reclassified $0.8 million of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the second public offering.
Restricted Cash	Restricted Cash At September 30, 2016 and December 31, 2015, restricted cash consisted of a certificate of deposit collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of September 30, 2016, the Company’s cash equivalents consisted of money market funds and U.S. government-sponsored enterprise securities.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s derivative liability, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying value of cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. In connection with the automatic conversion of the Company’s convertible preferred stock, which occurred upon the listing of the Company’s common stock on the NASDAQ on February 10, 2016, the preferred stock warrant became a warrant to purchase common stock and the liability was remeasured at fair value and reclassified to additional paid-in capital.
Net Income (Loss) per Share	Net Income (Loss) per Share In February 2016, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 9,699,600 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net loss per share as the Company had issued shares that met the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred stock contractually entitled the holders of such shares to participate in dividends, but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not to have been issued if their effect is anti-dilutive.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU No. 2016-02, Leases. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing (Topic 606) In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Short Term Investments (Tables)

Short Term Investments (Tables)	9 Months Ended
	Sep. 30, 2016
Cash Cash Equivalents And Short Term Investments [Abstract]
Summary of Short Term Investments	The following table summarizes the Company’s short term investments as of September 30, 2016 (in thousands): September 30, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 48,413 $ 2 $ (9 ) $ 48,406 U.S. treasury securities 8,008 — (2 ) 8,006 $ 56,421 $ 2 $ (11 ) $ 56,412

Fair Value of Financial Asset20

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of September 30, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 24,366 $ — $ — $ 24,366 U.S. government-sponsored enterprise securities — 16,466 — 16,466 Short-term investments: U.S. government-sponsored enterprise securities — 48,406 — 48,406 U.S. treasury securities — 8,006 — 8,006 $ 24,366 $ 72,878 $ — $ 97,244 Liabilities: Derivative liability $ — $ — $ 142 $ 142 $ — $ — $ 142 $ 142 Fair Value Measurements as of December 31, 2015 Using: Level 1 Level 2 Level 3 Total Liabilities: Derivative liability $ — $ — $ 2 $ 2 Preferred stock warrant liability — — 110 110 $ — $ — $ 112 $ 112
Assumptions and Inputs were Used in Determining Fair Value of Preferred Stock Warrant Liability	The following assumptions and inputs were used in determining the fair value of the preferred stock warrant liability valued using the Black-Scholes option-pricing model: As As of December 31, 2016 2015 Expected term (in years) 2.25 2.5 Expected volatility 73.24% 59.12% Risk-free interest rate 0.74% 1.21% Expected dividend yield 8.0% 8.0%
Summary of Changes in Values of Preferred Stock Warrant Liability and Derivative Liability	Changes in the values of the preferred stock warrant liability and the derivative liability are summarized below (in thousands): Preferred Stock Derivative Warrant Liability Liability Fair value at December 31, 2015 $ 110 $ 2 Change in fair value (82 ) 140 Conversion to common stock warrant (28 ) — Fair value at September 30, 2016 $ — $ 142

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2016
Text Block [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): September 30, December 31, 2016 2015 Accrued payroll and related expenses $ 1,469 $ 1,607 Accrued research and development expenses 1,810 185 Accrued professional fees 711 436 Accrued other 192 20 $ 4,182 $ 2,248

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense	Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended September Nine Months Ended September 30, 2016 2015 2016 2015 Research and development $ 119 $ 63 $ 351 $ 2 General and administrative 451 60 1,024 159 $ 570 $ 123 $ 1,375 $ 161

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2016
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September Nine Months Ended September 30, 2016 2015 2016 2015 Numerator: Net loss $ (10,771 ) $ (7,050 ) $ (27,815 ) $ (19,409 ) Modification of Series A preferred stock — 174 — 10,739 Accruing dividends on preferred stock — (2,459 ) (1,378 ) (6,698 ) Net loss attributable to common stockholders-basic and diluted $ (10,771 ) $ (9,335 ) $ (29,193 ) $ (15,368 ) Denominator: Weighted average number of common shares outstanding—basic 20,073,685 556,567 16,672,368 547,816 Net loss per share attributable to common stockholders—basic and diluted $ (0.54 ) $ (16.77 ) $ (1.75 ) $ (28.05 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding	The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported : As of September 30, 2016 2015 Convertible preferred stock (as converted to common stock) — 9,699,600 Options to purchase common stock 1,731,823 866,082 Warrant for the purchase of convertible preferred stock (as converted to common stock) 14,800 14,800 1,746,623 10,580,482

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jan. 19, 2016	Sep. 30, 2016USD ($)$ / sharesshares	Feb. 29, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Nature Of Business [Line Items]
Accumulated deficit | $		$ (148,033)		$ (148,033)	$ (120,218)
Cash, cash equivalents and short-term investments | $		$ 100,200		$ 100,200
Reverse stock split description				On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock.
Reverse stock split ratio	10.8102
Reverse stock split effective date				Jan. 19, 2016
Proceeds from IPO, net of underwriting discounts, commissions, and other offering expenses | $				$ 46,500
Number of shares converted | shares			9,699,600
Number shares issued in share conversion | shares			2,590,742
Preferred stock, authorize for future issuance | shares		5,000,000		5,000,000	0
Preferred stock, par value | $ / shares		$ 0.001		$ 0.001	$ 0.001
Preferred stock, issued | shares		0		0	0
Preferred stock, outstanding | shares		0		0	0
Proceeds from stock issuance, net of underwriting discounts, commissions, and other offering expenses | $				$ 70,265
IPO [Member]
Nature Of Business [Line Items]
Common stock issued and sold | shares			6,250,000
Common stock price per share | $ / shares			$ 8
Proceeds from IPO, net of underwriting discounts, commissions, and other offering expenses | $			$ 42,500
Underwriting discounts and commissions | $			3,500
Other offering expenses | $			4,000
Preferred stock, authorize for future issuance | shares		5,000,000		5,000,000
Preferred stock, par value | $ / shares		$ 0.001		$ 0.001
Preferred stock, issued | shares		0		0
Preferred stock, outstanding | shares		0		0
Follow-on Public Offering [Member]
Nature Of Business [Line Items]
Common stock issued and sold | shares		5,750,000
Common stock price per share | $ / shares		$ 13		$ 13
Underwriting discounts and commissions | $		$ 4,500
Other offering expenses | $		800
Proceeds from stock issuance, net of underwriting discounts, commissions, and other offering expenses | $		$ 69,500
Over Allotment [Member]
Nature Of Business [Line Items]
Common stock issued and sold | shares		750,000
Over Allotment [Member] | Maximum [Member]
Nature Of Business [Line Items]
Period granted for purchase of additional shares		30 days
Series A Preferred Stock [Member]
Nature Of Business [Line Items]
Accrued dividends | $			$ 36,000

Summary of Significant Accoun25

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Feb. 29, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Deferred offering costs			$ 2,744
Reclassification of deferred offering costs to additional paid-in capital	$ 800	$ 4,000
Number of common shares issued on conversion of convertible preferred stock		9,699,600

Short Term Investments - Summar

Short Term Investments - Summary of Short Term Investments (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 56,421,000
Gross Unrealized Gains	2,000
Gross Unrealized Losses	(11,000)
Fair Value	56,412,000	$ 0
U.S Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,413,000
Gross Unrealized Gains	2,000
Gross Unrealized Losses	(9,000)
Fair Value	48,406,000
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,008,000
Gross Unrealized Losses	(2,000)
Fair Value	$ 8,006,000

Short Term Investments - Additi

Short Term Investments - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Realized gains (losses) on short-term investments	$ 0	$ 0
Other-than-temporary impairments recognized	0	0
Short-term investments	$ 56,412,000	$ 56,412,000	$ 0

Fair Value of Financial Asset28

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Assets:
Cash equivalents		$ 0
Short-term investments		0
Liabilities:
Derivative liability	$ 142,000	2,000
Preferred stock warrant liability		110,000
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets	97,244,000
Liabilities:
Derivative liability	142,000	2,000
Preferred stock warrant liability		110,000
Total liabilities	142,000	112,000
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total assets	24,366,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Total assets	72,878,000
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Liabilities:
Derivative liability	142,000	2,000
Preferred stock warrant liability		110,000
Total liabilities	142,000	$ 112,000
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	24,366,000
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	24,366,000
Fair Value, Measurements, Recurring [Member] | U.S Government-Sponsored Enterprise Securities [Member]
Assets:
Cash equivalents	16,466,000
Short-term investments	48,406,000
Fair Value, Measurements, Recurring [Member] | U.S Government-Sponsored Enterprise Securities [Member] | Level 2 [Member]
Assets:
Cash equivalents	16,466,000
Short-term investments	48,406,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Assets:
Short-term investments	8,006,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Level 2 [Member]
Assets:
Short-term investments	$ 8,006,000

Fair Value of Financial Asset29

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Cash equivalents		$ 0
Short-term investments		0
Transfer of assets from level 1 to level 2	$ 0	0
Transfer of assets from level 2 to level 1	0	0
Transfer of liabilities from level 1 to level 2	0	0
Transfer of liabilities from level 2 to level 1	$ 0	$ 0
Fair value determination model	Monte-Carlo simulation analysis
Expected term	2 years 6 months	1 month 13 days
Expected volatility	81.50%	74.10%
Risk-free interest rate	0.82%	0.14%

Fair Value of Financial Asset30

Fair Value of Financial Assets and Liabilities - Assumptions and Inputs were Used in Determining Fair Value of Preferred Stock Warrant Liability (Detail)	Feb. 10, 2016	Dec. 31, 2015	Sep. 30, 2016	Dec. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term (in years)			2 years 6 months	1 month 13 days
Expected volatility			81.50%	74.10%
Risk-free interest rate			0.82%	0.14%
Preferred Stock Warrant Liability [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term (in years)	2 years 3 months	2 years 6 months
Expected volatility	73.24%	59.12%
Risk-free interest rate	0.74%	1.21%
Expected dividend yield	8.00%	8.00%

Fair Value of Financial Asset31

Fair Value of Financial Assets and Liabilities - Summary of Changes in Values of Preferred Stock Warrant Liability and Derivative Liability (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Preferred Stock Warrant Liability, Fair value, Beginning Balance	$ 110
Preferred Stock Warrant Liability, Change in fair value	(82)	$ 77
Preferred Stock Warrant Liability, Conversion to common stock warrant	(28)
Derivative Liability, Fair value, Beginning Balance	2
Derivative Liability, Change in fair value	140
Derivative Liability, Fair value, Ending Balance	$ 142

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 1,469	$ 1,607
Accrued research and development expenses	1,810	185
Accrued professional fees	711	436
Accrued other	192	20
Total accrued expenses	$ 4,182	$ 2,248

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Feb. 03, 2016	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense					$ 1,375,000	$ 161,000
Reduction in stock-based compensation expense						$ 500,000
Prior to 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in stock-based compensation expense				$ 200,000
Adjustments For Immaterial Errors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in stock-based compensation expense				$ 300,000
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options unvested		83,250			83,250
Fair value of option					$ 1,100,000
Stock option grants			0			0
Stock-based compensation expense, granted		$ 100,000			$ 100,000
Non-Employees [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grants		12,103			12,103
Non-Employees [Member] | Prior to 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option issued to purchase common stock					203,964
Stock-based compensation expense		$ 0			$ 0
Non-Employees [Member] | Prior to 2013 [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ (100,000)			$ (100,000)
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	1,581,839
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	3.00%
Common stock available for issuance		1,260,609			1,260,609
2016 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	138,757
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	1.00%
Common stock available for issuance		138,757			138,757

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 570	$ 123	$ 1,375	$ 161
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	119	63	351	2
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 451	$ 60	$ 1,024	$ 159

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Astellas Pharma Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 0.8	$ 1
Term of agreement	3 years 6 months	3 years 6 months
Biogen Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research funding payments on guaranteed basis			$ 4

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Federal income tax benefit	$ 0	$ 0
State income tax benefit	$ 0	$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net loss	$ (10,771)	$ (7,050)	$ (27,815)	$ (19,409)
Modification of Series A preferred stock		174		10,739
Accruing dividends on preferred stock		(2,459)	(1,378)	(6,698)
Net loss attributable to common stockholders-basic and diluted	$ (10,771)	$ (9,335)	$ (29,193)	$ (15,368)
Denominator:
Weighted average number of common shares outstanding—basic	20,073,685	556,567	16,672,368	547,816
Net loss per share attributable to common stockholders—basic and diluted	$ (0.54)	$ (16.77)	$ (1.75)	$ (28.05)

Net Loss per Share - Schedule38

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding (Detail) - shares	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted weighted-average shares outstanding	1,746,623	10,580,482
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted weighted-average shares outstanding	1,731,823	866,082
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted weighted-average shares outstanding		9,699,600
Warrants to Purchase Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted weighted-average shares outstanding	14,800	14,800

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended
	May 31, 2016USD ($)
Contingencies And Commitments [Line Items]
Retainer fee	$ 2.5
Percentage of M&A transaction fee payable	1.00%
Dr. Stelios Papadopoulos [Member]
Contingencies And Commitments [Line Items]
Retainer fee	$ 0.2